The current state-of-the-art in anthropomorphic prosthetic hands, such as the iLimb, Bebionic, and Vincent designs, generally use an individual actuator for each finger in order to enable multiple grasping behaviours and postures. The ability to utilize various grasp types helps to improve the hold on various shaped objects or to position the hand in the appropriate posture to facilitate as wide a range of tasks as possible. Although each style of prosthetic has its own strategy, these devices rely on myoelectric sequences, co-contractions or patterns to preselect the type of grasp. Many researchers have studied possible strategies to give quick and easy grasp selection including state-space trees and highly tuned pattern recognition software. The large variation in grasp types is what gives these myoelectric hands increased utility over single degree of freedom myoelectric hands.
Despite achieving various grasp types, it is still difficult for users of myoelectric hands to modulate grip force due to the lack of feedback from the hand. Body-powered devices, which are actuated through the upper arm or shoulders, are much easier to operate in terms of modulating grip force. This is largely due to the “feel” of the grasp as a result of the force exerted on the shoulder from the harness. They are also simpler and more robust than the multi-degree of freedom offered by myoelectric devices. Until now, body-powered devices have been restricted to operating a single degree of freedom, as in the body-powered split hook, or to open and close an anthropomorphic hand in a single grasp motion.
A major difficulty in the actuation of body-powered anthropomorphic prosthetic hands lies in the distribution of force from the body-powered cable to the five fingers. The simplest method is to couple all the fingers together into a single combined motion. This results in a single degree of freedom terminal device that is capable of performing a single grasp type. Although it is mechanically simple, other coupling methods can be used to allow for multiple grasping types and adaptive grip behaviour. Underactuation has shown advantages in robotic grasping, including better power grasping, more adaptive behaviour to various object types and shapes, and an increase in the number of contacts made on objects (Ohdner L U et al., Int J Robot Res, 2014). Many researchers have turned to relying on underactuated adaptive transmission systems to distribute load from a single actuation source to multiple fingers of the hand (Baril M et al., Proceedings of the ASME/IDETC/CEI, 2010).
There is a need in the art for a prosthetic hand capable of multiple grasp types with improved grasping performance. The present invention meets this need.